Method for controlling a multi-pulse record waveform at high velocity in a phase change optical medium

ABSTRACT

In an optical recording method and apparatus of the present invention, a driving power is applied to a light source to control emission of a light beam to a recording layer of an optical storage medium, the driving power including a sequence of mark and space portions, each mark portion having a pulse width that corresponds to a multiple of a period T of a write clock. A multi-pulse waveform of each mark portion of the driving power includes a front-end portion, a multi-pulse portion and a tail-end portion, the front-end portion having a first pulse width t 1  with a high-power write level Pw and starting from a middle-power erase level Pe, the multi-pulse portion including write pulses each having a second pulse width t 2  with the write level Pw and a third pulse width t 3  with a low-power base level Pb, the multi-pulse portion having a duty ratio z=t 2 /(t 2 +t 3 ), and the tail-end portion having a fourth pulse width t 4  with the base level Pb and ending at the erase level Pe. The waveform is controlled, when a linear velocity of rotation of the medium is set in a range higher than 5.6 m/s and up to 28 m/s, such that the first pulse width t 1  ranges 0.1T to 1T and the fourth pulse width t 4  ranges 0.2T to 1.3T.

This application is a divisional of application Ser. No. 10/638,500,filed Aug. 12, 2003, which is a continuation of application Ser. No.09/795,436, filed Mar. 1, 2001, now U.S. Pat. No. 6,631,109, issued Oct.7, 2003, which are all hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical recording method andapparatus that records information onto an optical storage modium at ahigh speed by emitting a light beam to a recording layer of the storagemedium. Further, the present invention relates to an optical storagemedium that stores information recorded by using the optical recordingmethod and apparatus.

2. Description of the Related Art

Recently, optical storage media, including CD-R (compact diskrecordable), CD-RW (compact disk rewritable) and so on, becomewidespread. Bach storage medium is provided for recording informationthereon by focusing a light beam onto a recording layer of the mediumand changing the phase of the recording layer material.

As disclosed in Japanese Laid-Open Patent Application No.63-29336, anoptical recording method that records information onto a recording layerof an optical recording medium by emitting light to the recording layerof the medium is known. In the optical recording method of the abovedocument, a light source driving waveform is applied to a light sourceto control emission of a light beam to the recording layer of the mediumbased on a write data modulation method. Moreover, there is known anoptical recording method that determines an optimum light source drivingwaveform (including the write power and the write pulse width), which isapplied to the light source, based on a readout signal of the recordedinformation derived from a reflection light beam from the optical disk.

Further, several optical recording methods have been proposed forimprovement of the quality of the write signal recorded on a rewritablephase-change storage medium. For example, Japanese Laid-Open PatentApplication No.63-266632 discloses such improvement method. In theconventional method of the above document, a pulse width modulation(PWM) method is utilized for application of a multi-pulse light sourcedriving waveform to the light source to control emission of a light beamfrom the light source to a rewritable phase-change optical disk having arecording layer with a large crystallization speed. The conventionalmethod provides the driving waveform that is effective in recording along amorphous mark on the recording layer of the optical disk.

In addition, Japanese Laid-Open Patent Application No.63-266633 and U.S.Pat. No. 5,150,352 disclose an optical recording method which eliminatespositional variations of a mark edge and improves the jittercharacteristics of an optical disk by applying a driving waveformincluding a front-end portion or a tail-end portion having an increasedpulse width or with an increased power level to the light source.

Further, the rewritable compact disk standards (the orange book, partIII, vet. 2.0) provide the recommended specifications of 1× to 4× linearvelocity recording of the rewritable recording media. The linearvelocities 1× to 4× according to the standards (the orange book, partIII, ver. 2.0) range from 1.2 m/s to 5.6 m/s. The recording speeds ofthe media in this range require a relatively long time to recordinformation onto the media. There is an increasing demand for a reliableCD-RW drive that is able to carry out error-free information recordingwith good write-erase characteristics at higher recording speeds.Preparations of high-speed specifications of range higher than 4× and upto 20× linear velocity recording for the rewritable compact diskstandards are now under way. The linear velocities range higher than 4×and up to 20× according to the standards (the orange book, part III)range higher than 5.6 m/s and up to 28 m/s.

Accordingly, it is desirable to provide an optical recording method andapparatus that ensures good write/erase characteristics of therewritable phase-change medium and retains the compatibility with thewrite-once storage medium when high-speed recording (equivalent to therange higher than 4× and up to 20× linear velocity recording) isperformed. The conventional recording methods and devices of the abovedocuments are not yet adequate to attain the goal.

SUMMARY OF THE INVENTION

It is a general object of the present invention to provide an opticalrecording method and apparatus in which the aforementioned problems areeliminated.

Another object of the present invention is to provide an opticalrecording method and apparatus that ensures good write/erasecharacteristics of the rewritable phase-change medium and retains thecompatibility with the write-once storage medium when high-speedrecording is performed.

Another object of the present invention is to provide an opticalrecording method and apparatus that provides increases of initialcharacteristics and overwrite performance of the rewritable phase-changemedium.

Another object of the present invention is to provide an optical storagemedium that stores information recorded by using the optical recordingmethod and apparatus such that good write/erase characteristics of therewritable phase-change medium arc ensured and the compatibility withthe write-once storage medium is retained when high-speed recording isperformed.

The above-mentioned objects of the present invention are achieved by anoptical recording method which records a sequence of data blocks onto arecording layer of an optical recording medium by emitting light to therecording layer of the medium and changing a phase of a recordingmaterial of the recording layer, the method comprising the steps of:applying a light source driving power to a light source to controlemission of a light beam to the recording layer of the medium, thedriving power including a sequence of mark and space portions, each markportion having a pulse width that corresponds to a multiple of a periodT of a write clock based on a write data modulation method; setting amulti-pulse waveform of each mark portion of the driving power thatincludes a front-end portion, a multi-pulse portion and a tail-endportion, the front-end portion having a first pulse width t1 with ahigh-power write level Pw and starting from a middle-power erase levelPe, the multi-pulse portion including a sequence of write pulses eachhaving a second pulse width t2 with the write level Pw and a third pulsewidth t3 with a low-power base level Pb, the multi-pulse portion havinga given duty ratio z=t2/(t2+t3), and the tail-end portion having afourth pulse width t4 with the base level Pb and ending at the eraselevel Pe; setting a linear velocity of rotation of the medium at acontrolled speed; and controlling the waveform when the linear velocityof rotation of the medium is set in a high-speed range higher than 5.6m/s and up to 28 m/s, such that the first pulse width t1 of thefront-end portion ranges 0.1T to 1T and the fourth pulse width t4 of thetail-end portion ranges 0.2T to 1.3T.

The above-mentioned objects of the present invention are achieved by anoptical recording apparatus which records a sequence of data blocks ontoa recording layer of an optical recording medium by emitting light tothe recording layer of the medium and changing a phase of a recordingmaterial of the recording layer, the apparatus comprising: a lightsource driver unit which applies a light source driving power to a lightsource to control emission of a light beam to the recording layer of themedium, the driving power including a sequence of mark and spaceportions, each mark portion having a pulse width that corresponds to amultiple of a period T of a write clock based on a write data modulationmethod; a write power determination unit which sets a multi-pulsewaveform of each mark portion of the driving power that includes afront-end portion, a multi-pulse portion and a tail-end portion, thefront-end portion having a first pulse width t1 with a high-power writelevel Pw and starting from a middle-power erase level Pe, themulti-pulse portion including a sequence of write pulses each having asecond pulse width t2 with the write level Pw and a third pulse width t3with a low-power base level Pb, the multi-pulse portion having a givenduty ratio z=t2/(t2+t3), and the tail-end portion having a fourth pulsewidth t4 with the base level Pb and ending at the erase level Pe; and acontroller which sets a linear velocity of rotation of the medium at acontrolled speed, wherein the controller causes the write powerdetermination unit to control the waveform when the linear velocity ofrotation of the medium is set in a high-speed range higher than 5.6 m/sand up to 28 m/s, such that the first pulse width t1 of the front-endportion ranges 0.1T to 1T and the fourth pulse width t4 of the tail-endportion ranges 0.2T to 1.3T.

The above-mentioned objects of the present invention are achieved by anoptical storage medium which stores information recorded by using anoptical recording method that records a sequence of data blocks onto arecording layer of an optical recording medium by emitting light to therecording layer of the medium and changing a phase of a recordingmaterial of the recording layer, the optical recording method comprisingthe steps of: applying a light source driving power to a light source tocontrol emission of a light beam to the recording layer of the medium,the driving power including a sequence of mark and space portions, eachmark portion having a pulse width that corresponds to a multiple of aperiod T of a write clock based on a write data modulation method;setting a multi-pulse waveform of each mark portion of the waveform thatincludes a front-end portion, a multi-pulse portion and a tail-endportion, the front-end portion having a first pulse width t1 with ahigh-power write level Pw and starting from a middle-power erase levelPe, the multi-pulse portion including a sequence of write pulses eachhaving a second pulse width t2 with the write level Pw and a third pulsewidth t3 with a low-power base level Pb, the multi-pulse portion havinga given duty ratio z=t2/(t2+t3), and the tail-end portion having afourth pulse width t4 with the base level Pb and ending at the eraselevel Pe; setting a linear velocity of rotation of the medium at acontrolled speed; and controlling the waveform when the linear velocityof rotation of the medium is set in a high-speed range higher than 5.6m/s and up to 28 m/s, such that the first pulse width t1 of thefront-end portion ranges 0.1T to 1T and the fourth pulse width t4 of thetail-end portion ranges 0.2T to 1.3T, the optical storage mediumcomprising the sequence of data blocks recorded on the recording layer,each data block including first information indicative of the firstpulse width t1 of the front-end portion and second informationindicative of the fourth pulse width t4 of the tail-end portion in thelight source driving waveform.

In the optical recording method and apparatus of the present invention,the driving power is applied to the light source to control emission ofa light beam to the recording layer of the optical storage medium, thedriving power including a sequence of mark and space portions, each markportion having a pulse width that corresponds to a multiple of theperiod T of the write clock. The waveform of each mark portion of thedriving power includes the front-end portion, the multi-pulse portionand the tail-end portion, the front-end portion having the first pulsewidth t1 with the write level Pw and starting from the erase level Pe,the multi-pulse portion including the write pulses each having thesecond pulse width t2 with the write level Pw and the third pulse widtht3 with the base level Pb, the multi-pulse portion having the duty ratioz=t2/(t2+t3), and the tail-end portion having the fourth pulse width t4with the base level Pb and ending at the erase level Pe. The waveform iscontrolled, when the linear velocity of rotation of the medium is set ina range higher than 5.6 m/s and up to 28 m/s, such that the first pulsewidth t1 ranges 0.1T to 1T and the fourth pulse width t4 ranges 0.2T to1.3T. As the front-end edge and the tail-end edge of each mark (theamorphous phase) are accurately and definitely created on the recordinglayer of the rewritable phase-change medium when high-speed recording isperformed, the optical recording method and apparatus of the presentinvention can ensure good write/erase characteristics of the rewritablephase-change medium and retain the compatibility with the write-oncestorage medium when high-speed recording is performed. The opticalrecording method and apparatus of the present invention are effective inincreasing the initial characteristics and the overwrite performance ofthe rewritable phase-change medium.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention willbecome apparent from the following detailed description when read inconjunction with the accompanying drawings.

FIG. 1 is a cross-sectional diagram of one preferred embodiment of theoptical storage medium of the invention.

FIG. 2 is a diagram for explaining a characteristic of storage medium'sreflectivity with respect to relative velocity and a characteristic ofthe differential coefficient of the reflectivity with respect torelative velocity.

FIG. 3 is a block diagram of one preferred embodiment of the opticalrecording apparatus of the invention.

FIG. 4A and FIG. 4B are waveform diagrams for explaining a multi-pulselaser driving waveform used by the optical recording apparatus of FIG.3.

FIG. 5 is a diagram for explaining the dependence of the write signalasymmetry on the front-end pulse width and the tail-end pulse width ofthe multi-pulse waveform.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A description will now be provided of preferred embodiments of thepresent invention with reference to the accompanying drawings.

FIG. 1 is a cross-sectional diagram of one preferred embodiment of theoptical storage medium of the invention.

The optical storage medium of the present embodiment is a rewritablephase-change medium (CD-RW) in which a recording layer of a phase-changematerial is formed on a substrate. As shown in FIG. 1, in the storagemedium 1 of this embodiment, a substrate 2, a lower protective layer 3,a recording layer 4, an upper protective layer 5, and areflection/heat-radiation layer 6 are provided. The lower protectivelayer 3, the recording layer 4, the upper protective layer 5 and thereflection/heat-radiation layer 6 are deposited, in this order, on thefront surface of the substrate 2. Further, an over-coat layer 7 may beprovided on the reflection/heat-radiation layer 6, and a hard-coat layer8 may be provided on the back surface of the substrate 2.

In the medium 1 of the present embodiment, the substrate 2 is providedin order to support the recording layer 4. When a read/write laser beamemitted by a laser light source is incident to the substrate 2 of thestorage medium 1, the substrate 2 must be transparent to the incidentlaser beam having a wavelength of the read/write laser beam used. Asuitable transparent material of the substrate 2 is selected from amongglass materials, ceramics materials and resin materials. Resin materialsare more suitable for the substrate 2 because of the transparency andthe ease of molding.

A suitable resin material of the substrate 2 may be selected from one ofresin materials including polycarbonate resins, acrylic resins, epoxyresins, polystyrene resins, styrene-acrylonitrile copolymer resins,polyethylene resins, polypropylene resins, silicon-based resins,fluorine-based resins, acrylonitrile-butadiene-styrene (ABS) resins andurethane resins. In particular, polycarbonate resins or acrylic resinsarc selected as a more suitable material of the substrate 2, because ofthe ease of molding, the required optical characteristics and the costeffectiveness. A set of guide grooves may be provided on the transparentsubstrate 2.

In the storage medium 1 of the present embodiment, the lower and upperprotective layers 3 and 5 are made of a dielectric material because ofthe required thermal and optical characteristics. A suitable material ofthe protective layers 3 and 5 may be selected from a single-component ormixture dielectric materials including oxides of SiO₂, SiO, ZnO, SnO₂,TiO₂, InO₂, Mg, ZrO₂, etc., nitrides of Si₃N₄, AlN, TiN, BN, ZrN, etc.,sulphides of ZnS, In₂S₃, TaS₄, etc., carbides of SiC, TaC, B4C, WC, TiC,ZrC, etc., and diamond-state carbon. The lower and upper protectivelayers 3 and 5 are deposited by using physical vapor deposition,sputtering, ionplating, or chemical vapor deposition. Because of theproductivity and the cost, sputtering is selected as the more suitableone for the formation of the lower and upper protective layers 3 and 5.An optimum thickness of the protective layers 3 and 5 may be determinedin view of the required thermal and optical characteristics. Typically,the thickness of the protective layers 3 and 5 ranges from 10 nm to 5000nm.

In the storage medium 1 of the present embodiment, the recording layer 4is made of a phase-change material. A suitable phase-change material ofthe recording layer 4 may be selected from alloy-based phase-changematerials including GeTe, GeTeSe, GeTeS, GeSeSb, GeAsSe, InTe, SeTe,SeAs, Ge—Te—(Sn, Au, Pd), GeTeSeSb, GeTeSb, AgInSbTe, etc. Thecomposition of elemental substances in each phase-change material may beoptimized in accordance with a linear velocity of rotation of themedium. A small amount of impurities, selected from substances includingB, N, C, O, Si, P, S, Ge, Se, Al, Ti, Zr, V, Mn, Fe, Co, Ni, Cr, Cu, Zn,Sn, Pd, Pt, Au, etc., may be mixed with the phase-change material of therecording layer 4.

Specifically, the selection of AgInSbTe as the phase-change material ofthe recording layer 4 is more suitable because it provides definiteboundaries between crystalline areas and non-crystalline (or amorphous)areas, which suits to a mark-edge recording technique (which will bedescribed later) that is used by the optical recording method andapparatus of the present invention. A small amount of impurities (forexample, N) may be added to the phase-change material, which allows amargin of the linear velocity of the medium rotation to be increased.

In the storage medium 1 of the present embodiment, the composition ofthe phase-change material (AgInSbTe) of the recording layer 4 isrepresented by the formula Ag_(α)In_(β)Sb_(γ)Te_(δ)

-   -   0.1≦α≦3.0    -   5.0≦β≦12.0    -   60.0≦γ≦72.0    -   22.0≦δ≦30.0        A desired thickness of the phase-change material of the        recording layer 4 ranges from 13 nm to 17 nm. With the above        composition and the above thickness of the phase-change material        of the recording layer 4, the present embodiment can ensure good        write/erase characteristics of the rewritable phase-change        medium and retain the compatibility with the write-once storage        medium even when high-speed recording is performed.

In the storage medium 1 of the present embodiment, the recording layer 4is deposited on the substrate 2 by using physical vapor deposition,sputtering, ionplating, or chemical vapor deposition. Because of theproductivity and the cost, sputtering is selected as the more suitableone for the formation of the recording layer 4.

Further, in the storage medium 1 of the present embodiment, thereflection/heat radiation layer 6 serves to reflect the read/write lightbeam and dissipate heat produced during recording. A suitable materialof the reflection/heat radiation layer 6 may be selected fromsingle-component metals Including Ag, Au, Al, or mixture alloysincluding Ti, Si, Cr, Ta, Cu, Pd, C, etc. Preferably, thereflection/heat radiation layer 6 is made of an aluminum-based alloybecause of the required thermal and optical characteristics and theproductivity. A desired composition of the material of thereflection/heat radiation layer 6 and a desired thickness of thereflection/heat radiation layer 6 may be determined in view of therequired thermal and optical characteristics.

In the storage medium 1 of the present embodiment, the over-coat layer 7is made of a resin material containing, as the major component, anoptical curing resin or an electron beam curing resin. Because of theease of curing and the case of film formation, a resin materialcontaining, as the major component, a UV (ultraviolet ray) curing resinis more suitable for the material of the over-coat layer 7. The filmformation of the over-coat layer 7 is performed by using a dippingmethod or a spin-coat method.

In order to conform to the high-speed specifications of range higherthan 4× and up to 20× linear velocity recording for the expectedrewritable compact disk standards, it is necessary that the opticalstorage medium 1 of the present embodiment be configured to meet theconditions related to the phase-change critical linear velocity (whichwill be called the velocity “vo”).

Suppose that a measuring device (or a pickup) for measuring thephase-change critical linear velocity (the velocity “vo”) of the mediummeets the following conditions: the wavelength of a read/write laserbeam emitted by the laser light source is 789 nm; and the numericalaperture (NA) of the objective lens is 0.49. Further, suppose that “v”indicates a relative velocity of the medium to the optical recordingapparatus during the recording, “vwh” indicates the highest relativevelocity of the medium during the recording, and “vwl” indicates thelowest relative velocity of the medium during the recording.

A measurement power “P_(E)” of the measuring device (or the pickup) usedwhen measuring the velocity “vo” of the medium is defined by theformula: P_(E)=0.75 P_(OH) where “P_(OH)” indicates an optimum recordingpower when the linear velocity “v” of the medium 1 is set at the highestlinear velocity “vwh”.

The measurement of the velocity “vo” is performed when the medium 1 ismoved to the pickup at the relative velocity “v” and the pickup emits awrite laser beam to the medium from the laser light source at themeasurement power “P_(E)”. At this time, a pulsed light source emissionwaveform, which is ordinarily used for the recording of conventionalphase-change media, is not used for the emission of the laser beam. Adirect-current (DC) driving waveform is used for the emission of thewrite laser beam, and a reflectivity of the recorded portion of themedium is detected based on a reflection beam from the medium by areproducing part of the optical recording apparatus. The reflectivityobtained at this time is indicated by a variable R(v) with respect tothe relative velocity “v”. Suppose that the wavelength of the read laserbeam is set at 789 nm.

FIG. 2 shows a characteristic of the reflectivity “R” of the medium 1 ofthe present embodiment with respect to the relative velocity “v” and acharacteristic of the differential coefficient “−dR/dv” of thereflectivity with respect to relative velocity “v”.

As shown in FIG. 2, as the relative velocity “v” increases, thereflectivity “R” decreases from an initial saturation point “R_(A)”.When a certain point of the relative velocity “v” is reached, thedecrease of the reflectivity “R” is stopped at a secondary saturationpoint “R_(B)”. Conversely, as the relative velocity “v” decreases, thereflectivity “R” increases from the secondary saturation point R_(B),and when a certain point of the relative velocity “v” is reached, theincrease of the reflectivity “R” is stopped at the initial saturationpoint R_(A).

As is apparent from FIG. 2, the phase-change critical relative velocity“vo” of the medium is defined by a value of the relative velocity “v”when the differential coefficient “−dR/dv” of the reflectivity is themaximum “(−dR/dv)max” (the peak point). A margin “Δvo” of the velocity“vo” is defined by an effective range of the linear velocity “v” whenthe differential coefficient “−dR/dv” of the reflectivity decays to halfthe maximum “(−dR/dv)max”.

In the storage medium 1 of the present embodiment, the phase-changematerial of the recording layer is selected such that it satisfies thefollowing conditions:vo≧0.7 vwh

where “vo” is the phase-change critical linear velocity, and “vwh” isthe highest linear velocity.

It has been confirmed from experiments that, when the optical storagemedium 1 of the present embodiment is configured to meet the aboveconditions (in other words, the velocity “vo” of the medium 1 is set tosatisfy the above conditions), the medium 1 provides good write/erasecharacteristics as well as improved overwrite performances when therecording is performed at the highest linear velocity “vwh”.

On the other hand, when the medium 1 does not meet the above conditions,it provides poor write/erase characteristics as well as undesiredoverwrite performances when the recording is performed at the highestlinear velocity “vwh”. The primary reason is that it is difficult thatsuch medium 1 returns the state of a mark on the medium with thereflectivity being at the secondary saturation point R_(B) back to thestate of a space on the medium with the reflectivity being at theinitial saturation point R_(A).

Further, in the storage medium 1 of the present embodiment, it ispreferred that the phase-change material of the recording layer isselected such that it satisfies the following conditions:vo≦3.0 vwl

where “vo” is the phase-change critical linear velocity, and “vwl” isthe lowest linear velocity.

It has been confirmed from experiments that, when the optical storagemedium 1 of the present embodiment is configured to meet the aboveconditions (in other words, the velocity “vo” of the medium 1 is set tosatisfy the above conditions), the medium 1 provides good mark-formationcharacteristics as well as improved overwrite performances when therecording is performed at the lowest linear velocity “vwl”.

The margin “Δvo” of the medium 1 indicates the tendency of deteriorationof the recording signal at the highest linear velocity “vwh”. In thestorage medium 1 of the present embodiment, it is preferred that thephase-change material of the recording layer is selected such that itsatisfies the following conditions:Δvo/vo<0.4

where “vo” is the phase-change critical linear velocity, and “Δvo” isthe margin of the velocity “vo”.

It has been confirmed from experiments that, when the optical storagemedium 1 of the present embodiment is configured to meet the aboveconditions (in other words, the velocity “vo” of the medium 1 is set tosatisfy the above conditions), the medium 1 provides improved stabilityof write/erase characteristics when the recording is performed at thehighest linear velocity “vwh”.

Further, in the storage medium 1 of the present embodiment, it ispreferred that the phase-change material of the recording layer isselected such that it satisfies the following conditions:0.1<R _(A) /R _(B)<0.6

where “R_(A)” is the initial saturation point of the medium, and “R_(B)”is the secondary saturation point of the medium.

It has boon confirmed from experiments that, when the optical storagemedium 1 of the present embodiment is configured to moot the aboveconditions, the medium 1 provides a good mark/space contrast when therecording is performed.

Further, in the storage medium 1 of the present embodiment, it ispreferred that the phase-change material of the recording layer isselected such that it satisfies the following conditions:vwh/vwl≧2.5

where “vwh” is the highest linear velocity of the medium during therecording, and “vwl” is the lowest linear velocity of the medium duringthe recording.

It has been confirmed from experiments that, when the optical storagemedium 1 of the present embodiment is configured to meet the aboveconditions, it makes it possible to perform the constant angularvelocity (CAV) recording of a 120-mm diameter optical disk (currentlythe dominating one) in the recording linear velocities corresponding tothe disk recording areas ranging from 46.5 mm diameter to 116 mmdiameter.

FIG. 3 shows one preferred embodiment of the optical recording apparatusof the invention. The optical recording apparatus of the presentembodiment is configured to conform to the high-speed specifications ofrange higher than 4× and up to 20× linear velocity recording for theexpected rewritable compact disk standards.

As shown in FIG. 3, in the optical recording apparatus of the presentembodiment, the optical storage medium 1 is held on and rotated by aspindle motor 11. A controller (CTRL)16 controls the spindle motor 11 sothat the linear velocity of rotation of the medium 1 is set at acontrolled speed. A pickup 12 having a laser light source (for example,a laser diode) and optical systems (for example, a focusing lens and anobjective lens) is provided to focus a laser beam, emitted by the lightsource, onto the recording layer of the medium 1 and change the phase ofthe recording material of the layer. The pickup 12 includes aphotodetector which detects a reflection laser beam reflected from therecording layer of the medium 1 and outputs a readout signal based onthe reflection laser beam.

In the optical recording apparatus of FIG. 3, a laser diode driver (LDD)13 is provided to apply a laser driving power to the light source of thepickup 12 to control the emission of a laser beam to the recording layerof the medium 1. When recording of the medium 1 is performed, the LDD 13applies the driving power to the light source of the pickup 12, and thelight source emits the laser beam to the recording layer of the medium 1to change the phase of the recording material of the layer. Whenreproducing of the medium 1 is performed, the photodetector of thepickup 12 detects the reflection laser beam reflected from the recordinglayer of the medium 1 and outputs the readout signal based on thereflection laser beam. In the optical recording apparatus of the presentembodiment, the readout signal output by the photodetector of the pickup12 is used to carry out the reproducing of the recorded information, thetracking servo control and the focusing servo control.

In the optical recording apparatus of FIG. 3, during the recording ofthe medium 1, the readout signal output by the pickup 12 is supplied toa write power monitoring unit (WPMU) 14. The write power monitoring unit14 monitors the readout signal received from the pickup 12. A writepower calculating unit (WPCU) 15 is provided to calculate the power (orthe amplitude) of the readout signal and outputs the calculation result(the calculated power) to the controller 16. The controller 16 has a CPU(central processing unit), which controls the elements of the opticalrecording apparatus of the present embodiment. As described above, thecontroller 16 controls the rotating speed of the spindle motor 12 sothat the linear velocity of rotation of the medium 1 is set at acontrolled speed.

In the optical recording apparatus of FIG. 3, a write powerdetermination unit (WPDU) 17 is provided to set a multi-pulse waveformof the laser driving power that is applied to the pickup 12. Thecontroller 16 outputs a control signal to the WPDU 17 based on thefeedback result (or the calculated power) from the MPCU 15, so that theWPDU 17 outputs a selected one of a test writing power (TWP) set signaland an optimum writing power (OWP) set signal to the LDD 13.

In the optical recording apparatus of the present embodiment, the pickup12, the LDD 13, the WPDU 17 and the controller 16 form an opticalinformation recording means 18. The optical information recording means18 carries out a mark-edge recording process for the storage medium 1wherein a sequence of data blocks (also called the write information),which corresponds to a sequence of mark and space portions of thedriving power, are recorded onto the recording layer of the medium 1,each of the mark portions having a pulse width corresponding to amultiple of a period (T) of a write clock based on a PWM (pulse widthmodulation) method. In a case of the rewritable phase-change medium(CD-RW), the optical information recording means 18 converts each datablock in the write information into a power level and a pulse width inthe driving waveform by using an EFM (eight to fourteen modulation)process or another improved modulation technique based on the period Tof the write clock.

In the optical recording apparatus of the present embodiment, the WPDU17 sets a multi-pulse laser waveform of the driving power in order tocontrol the emission of a laser beam by the laser light source of thepickup 12 to the recording layer of the medium 1 (CD-RW). FIG. 4A andFIG. 4B are waveform diagrams for explaining the multi-pulse laserdriving waveform used by the optical recording apparatus of FIG. 3.

FIG. 4A shows the waveform of a 5T input signal where “T” indicates theperiod of the write clock in the optical recording apparatus of FIG. 3.The “5T” input signal means that this pulsed signal has a pulse widththat is 5 times the period T of the write clock. In the example of FIG.4A, the high-level signal portion represents “1” of the writeinformation and corresponds to a mark on the recording layer of themedium 1, and the low-level signal portions represent “0” of the writeinformation and correspond to spaces on the recording layer of themedium 1.

FIG. 4B shows an example of the multi-pulse laser driving waveform thatis sot by the WPDU 17 of the present embodiment in response to the inputsignal of FIG. 4A.

As shown in FIG. 4A and FIG. 4B, the multi-pulse waveform, supplied fromthe WPDU 17 to the LDD 13, includes a front-end portion “fp”, amulti-pulse portion “mp” and a tail-end portion “op”. The front-endportion “fp” has a first pulse width “t1” with a high-power write level“Pw” and starts from a middle-power erase level “Pe”. The multi-pulseportion “mp” includes a sequence of write pulses each having a secondpulse width “t2” with the write level Pw and a third pulse width “t3”with a low-power base level “Pb”. Suppose that the conditions: Pb<Pe<Pware met. The multi-pulse portion “mp” has a given duty ratioz=t2/(t2+t3). The tail-end portion “op” has a fourth pulse width “t4”with the base level Pb and is ends at the erase level Pe.

Generally, when one of the mark portions of the driving power issupplied to the light source of the pickup 12, a non-crystalline area(the amorphous phase) that represents “1” of the write information isformed as a mark on the recording layer of the medium 1 by the emissionof a laser beam from the light source to the medium 1. The formation ofthe amorphous phase of the recording material on the recording layer ofthe medium 1 requires heating of the recording layer to an increasedtemperature above the melting point of the recording material andcooling of the recording layer for an adequate time after the heating.

In the waveform of FIG. 4B, the front-end portion “fp”, which has thefirst pulse width t1 with the high-power write level Pw, provides therecording layer of the medium 1 with the energy needed to heat it to theincreased temperature above the melting point. The multi-pulse portion“mp”, which includes the sequence of write pulses each having the secondpulse width t2 with the write level Pw and the third pulse width t3 withthe base level Pb, provides the recording layer with the energy neededto form the mark thereon. Hence, if the first pulse width t1 is set atan optimum value and the waveform of the present embodiment is applied,a front-end edge of the mark can be accurately and definitely formed onthe recording layer of the medium 1.

Further, in the waveform of FIG. 4B, the tail-end portion “op”, whichhas the fourth pulse width t4 with the low-power base level Pb, servesto cool the recording layer of the medium 1 for an adequate time afterthe heating. Hence, if the fourth pulse width t4 is set at an optimumvalue and the waveform of the present embodiment is applied, a tail-endedge of the mark can be accurately and definitely formed on therecording layer of the medium 1.

It is necessary to take into consideration the above points, in order toprovide good write/erase characteristics of the rewritable phase-changemedia when high-speed recording (equivalent to the range higher than 4×and up to 20× linear velocity recording) is performed. To attain theobjective of the present invention, the optical recording apparatus ofthe present embodiment is configured such that the controller 16 causesthe write power determination unit (WPDU) 17 to control the multi-pulsewaveform of FIG. 4B when the linear velocity of rotation of the medium 1is set in a high-speed range higher than 5.6 m/s and up to 28 m/s, suchthat the first pulse width “t1” of the front-end portion “fp” ranges0.1T to 1T and the fourth pulse width “t4” of the tail-end portion “op”ranges 0.2T to 1.3T. Optimum values of the first pulse width t1 and thefourth pulse width t4 vary depending on the recording material of therecording layer of the medium 1.

Experiments have been performed to ascertain the advantages of theoptical recording apparatus of the present embodiment that is configuredas described above. FIG. 5 shows the dependence of the write signalasymmetry on the front-end pulse width “t1” and the tail-end pulse width“t4” of the multi-pulse waveform.

In the present embodiment, the controller 16 causes the WPDU 17 tocontrol the waveform when the linear velocity of rotation of the medium1 is set in a high-speed range higher than 5.6 m/s and up to 28 m/s,such that the first pulse width t1 of the front-end portion ranges 0.1Tto 1T and the fourth pulse width t4 of the tail-end portion ranges 0.2Tto 1.3T. In order to examine the performances of high-speed recording,the experiments are performed under the following conditions.

A CD-RW disk that is provided in conformity with the above-describedembodiment of the optical storage medium of the invention is used forthe experiments, and the CD-RW disk is called the medium 1. Thewavelength of a laser beam emitted by the laser light source of thepickup 12 in the optical recording apparatus is 780 nm. The numericalaperture (NA) of the objective lens of the pickup 12 is set at 0.5. Ahigh-speed recording of the medium 1 is performed at 9.6 m/s linearspeed (which is equivalent to 8× linear velocity of the rewritablecompact disk standards).

As shown in FIG. 5, when performing the experiments, the first pulsewidth “t1” of the front-end portion “fp” of the multi-pulse waveform issequentially changed to one among 0.1T, 0.4T, 0.7T and 1.0T, and, at thesame time, the fourth pulse width “t4” of the tail-end portion “op” ofthe multi-pulse waveform is changed to one among 0.2T, 0.5T, 0.8T, 1.0Tand 1.3T with respect to each of the respective first pulse widthvalues. By performing the experiments, the dependence of the writesignal asymmetry on the front-end pulse width “t1” and the tail-endpulse width “t4” of the multi-pulse waveform is evaluated. FIG. 5 showssuch results of the evaluations. Generally, the write signal asymmetryindicates the degree of asymmetry of mark length and space length, andit is represented by a normalized value obtained by dividing adifference between the average level of the radio-frequency (RF) signalamplitude of the longest mark and the average level of the RF signalamplitude of the shortest mark by the RF signal amplitude of the longestmark.

The specifications of the rewritable compact disk standards provide therequirements: −15≦asymmetry≦5. As is apparent from the characteristicsof FIG. 5, in order to meet the requirements, it is necessary that thefront-end pulse width “t1” of the multi-pulse waveform ranges from 0.1Tto 1.0T and the tail-end pulse width “t4” of the multi-pulse waveformranges from 0.2T to 1.3T.

In another preferred embodiment of the optical recording method andapparatus of the invention, the optical storage medium 1 is prepared, inadvance, to contain a sequence of data blocks recorded on the recordinglayer, each data block including first information indicative of thefirst pulse width t1 of the front-end portion “fp” and secondinformation indicative of the fourth pulse width t4 of the tail-endportion “op” in the multi-pulse waveform. In the present embodiment,optimum values of the first pulse width t1 and the fourth pulse width t4that are suited to a specific phase-change material of each individualmedium 1 are predetermined. And, wobbling grooves or the like, carryingboth the first information and the second information are formed on themedium 1.

In the optical recording method and apparatus of the present embodiment,prior to a start of the recording of the medium 1, a test writingprocess is performed in which test data blocks are recorded onto atest-write region (for example, a power calibration area PCA) of themedium 1 and a readout signal is detected from the test-write region ofthe medium 1, the readout signal indicative of the first information andthe second information related to the test data blocks. Further, optimumvalues of the first pulse width t1 and the fourth pulse width t4 arecalculated based on the first information and the second informationindicated by the readout signal. In the present embodiment, themulti-pulse waveform is controlled based on the optimum values of thefirst pulse width t1 and the fourth pulse width t4.

According to the above-described embodiment, the optimum values of thefirst pulse width t1 and the fourth pulse width t4 in the multi-pulsewaveform can be suitably determined. As the recording of the medium 1can be performed in the optimum conditions, the optical recording methodand apparatus of the present embodiment are effective in preventing theoccurrence of a read error after the recording of the medium 1 isperformed, due to deterioration of the write signal quality of themedium 1.

Further, for the sake of convenience of the users, it is preferred tomake commercially available the optical storage medium 1 that isformatted, in advance, to contain the first information indicative ofthe first pulse width t1 of the front-end portion “fp” and the secondinformation indicative of the fourth pulse width t4 of the tail-endportion “op” in the multi-pulse waveform. The formatted medium 1 of thepresent embodiment provides the users with the ease-to-use feature aswell as good write/erase characteristics of the rewritable phase-changemedium when the high-speed recording is performed.

The present invention is not limited to the above-described embodiments,and variations and modifications may be made without departing from thescope of the present invention.

Further, the present invention is based on Japanese priority applicationNo.2000-058399, filed on Mar. 3, 2001, the entire contents of which arehereby incorporated by reference.

1. An optical storage medium in which information is recorded by using amulti-pulse waveform of a light source driving power, the multi-pulsewaveform including a front-end portion, a multi-pulse portion and atail-end portion, the front-end portion having a first pulse width t1with a high-power write level Pw and starting from a middle-power eraselevel Pe, the multi-pulse portion including a sequence of write pulseseach having a second pulse width t2 with the write level Pw and a thirdpulse width t3 with a low-power base level Pb, the multi-pulse portionhaving a given duty ratio z=t2/(t2+t3), the tail-end portion having afourth pulse width t4 with the base level Pb and ending at the eraselevel Pe, and when a linear velocity of rotation of the medium is setsubstantially in a speed range higher than 5.6 m/s and up to 28 m/s, thefirst pulse width t1 of the front-end portion ranging from 0.1T to 1Tand the fourth pulse width t4 of the tail-end portion ranging from 0.2Tto 1.3T where T is a period of a write clock, the optical storage mediumcomprising: a substrate; and at least one recording layer of aphase-change material formed on the substrate, wherein the multi-pulsewaveform of the driving power is applied to a laser light source tocontrol emission of a laser light beam to said at least one recordinglayer, and an amorphous phase of the phase-change material is formed bythe emission of the laser light beam so that the information is recordedin the medium and the recorded information can be reproduced from themedium.
 2. The optical storage medium of claim 1 wherein thephase-change material of said at least one recording layer is analloy-based phase-change material.
 3. The optical storage medium ofclaim 2 wherein a composition of the phase-change material of said atleast one recording layer is represented by the formulaAg_(α)In_(β)Sb_(γ)Te_(δ) 0.1≦α≦3.0 5.0≦β≦12.0 60.0≦γ≦72.0 22.0≦δ≦30.0.4. The optical storage medium of claim 3 wherein a small amount of N isadded to said phase-change material of said at least one recordinglayer.
 5. The optical storage medium of claim 1 wherein the medium has amulti-layer composition.
 6. The optical storage medium of claim 1wherein guide grooves are provided on the substrate.
 7. The opticalstorage medium of claim 1 wherein grooves carrying first informationindicative of the first pulse width t1 of the front-end portion in thewaveform are provided on the substrate.
 8. The optical storage medium ofclaim 1 wherein grooves carrying second information indicative of thefourth pulse width t4 of the tail-end portion in the waveform areprovided on the substrate.
 9. The optical storage medium of claim 1wherein the linear velocity of rotation of the medium is 9.6 m/s.
 10. Anoptical storage medium in which information is recorded by using amulti-pulse waveform of a light source driving power, the multi-pulsewaveform including a front-end portion, a multi-pulse portion and atail-end portion, the front-end portion having a first pulse width t1with a high-power write level Pw and starting from a middle-power eraselevel Pe, the multi-pulse portion including a sequence of write pulseseach having a second pulse width t2 with the write level Pw and a thirdpulse width t3 with a low-power base level Pb, the multi-pulse portionhaving a given duty ratio z=t2/(t2+t3), and the tail-end portion havinga fourth pulse width t4 with the base level Pb and ending at the eraselevel Pe, and the first pulse width t1 of the front-end portion ranging0.1T to 1T and the fourth pulse width t4 of the tail-end portion ranging0.2T to 1.3T where T is a period of a write clock, the optical storagemedium comprising: a substrate; and at least one recording layer of aphase-change material formed on the substrate, wherein the phase-changematerial is provided to satisfy the conditions: vwh/vwl≧2.5 where vwh isa highest linear velocity of the medium during the recording and vwl isa lowest linear velocity during the recording, wherein the multi-pulsewaveform of the driving power is applied to a laser light source tocontrol emission of a laser light beam to the recording layer, and anamorphous phase of the phase-change material is formed by the emissionof the laser light beam so that the information is recorded in themedium and the recorded information can be reproduced from the medium.